SOLUTION: solve this equation by completing the square -4r^2+21r=r+13

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Question 414893: solve this equation by completing the square -4r^2+21r=r+13

Answer by stanbon(75887) About Me  (Show Source):
You can put this solution on YOUR website!
solve this equation by completing the square
-4r^2+21r=r+13
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-4r^2 + 20r - 13 = 0
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r = [-20 +- sqrt(400 -4*-4*-13)]/(2*-4)
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r = [-20 +- sqrt(192)]/(-8)
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r = [-20 +- 8sqrt(2)]/(-8)
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r = (5/2) +- sqrt(2)
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Cheers,
stan H.